Variable stiffness electrically conductive composite,...

Details Variable stiffness electrically conductive composite,... Variable stiffness electrically conductive composite,...

2000-06-30

2003-05-13

Walberg, Teresa (Department: 3742)

Surgery

Means for introducing or removing material from body for...

Treating material introduced into or removed from body...

C606S007000

Reexamination Certificate

active

06562021

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to interventional medical devices, and more particularly concerns an electrically conductive, composite resistive heating catheter shaft having variable stiffness for enhanced performance of the composite shaft when used with or without a guide catheter, or as a stand-alone flow directed device for use in the vascular system as part of a therapeutic system or for delivery of medical devices.
2. Description of Related Art
Conventional minimally invasive catheter based therapies typically require guide wires that are one to two meters long extending through a longitudinal lumen in the catheter, and that are torqueable and pushable at the proximal end, yet soft and flexible at the distal end. Many such guidewires are made of stainless steel or the like, and are ground to tapers which provide the desired bending properties along the guidewire. Recently, numerous minimally invasive sensing and actuation procedures have been developed which utilize an optical fiber to deliver optical light or power to the distal tip of the optical fiber. For example, optical fiber based technology can be used for treatments such as “thrombolyzing” blood or cutting tissue by use of high energy light delivered through the end of the optical fibers, and for the delivery of therapeutic agents, such as timed release agents or embolics. However, conventional optical fiber technology has not been easily adaptable to such applications, particularly when the optical fiber must also act as a guidewire, either within a catheter or as a stand-alone device, since optical fibers, when used alone, are not very torqueable, pushable or resilient when compared to guide wires made from a variety of other, more rigid, materials. Also, small diameter optical fibers are quite “floppy” and in very small diameters are likely to kink, while larger diameter fibers which perform better in that regard can be too stiff to maneuver through sharp bends, and the use of optical fibers as guidewires or pushers within catheters can thus be difficult and quite technique sensitive.
A variable stiffness catheter having a longitudinal lumen is known that is composed of a relatively flexible outer coaxial tube and at least two tandemly disposed inner coaxial tube segments, the tube segments varying in stiffness, with the stiffest being located at the proximal end of the catheter and the least stiff ending proximal of the distal end of the catheter, thus providing the catheter with a minimum of two regions of different stiffness and flexibility. In order to reinforce a wide variety of catheters incorporating longitudinal lumens for interventional therapies, catheters in the prior art have used reinforcements to the exterior of the catheter, including additional strengthening layers and the like to alter the bending characteristics of the catheter. However, such a catheter structure is typically only capable of being used with a guidewire.
It would be desirable to provide an electrically conductive catheter shaft including one or more electrically conductive members with variable stiffness to be more pushable at the proximal end and more trackable at the distal end, and to make the use of such electrically conductive members in catheter-based therapies utilizing resistive heating more straightforward and less technique sensitive. The present invention addresses these and numerous other needs.
SUMMARY OF THE INVENTION
Briefly, and in general terms, the present invention in its broadest aspect provides for a variable stiffness electrically conductive composite, resistive heating catheter shaft, with a variable stiffness jacket encapsulating the shaft to make the use of such a shaft in catheter based therapies more predictable, straight forward, and less technique sensitive. Typically, such a shaft can be an electrically conductive member or the like which by itself has physical characteristics that are undesirable for guidewires or pusher devices. By use of the invention, a variable stiffness shaft can be made which is more pushable at the proximal end and more trackable at the distal end, with the capability to provide a wide range of predictable variations in stiffness and other structural parameters over the length of the shaft. It has been found that it is often the case that a catheter shaft such as an optical fiber or ultrasonic conductor member is made of a material that has undesirable characteristics for guidewires, since they are generally of a less resilient and strong material than those typically chosen for guidewires. The invention overcomes these limitations by providing for means to selectively strengthen the catheter shaft by low profile overlays of materials to create a composite shaft. A variable stiffness electrically conductive catheter shaft constructed according to the invention can be used in conjunction with a guide catheter or as a pusher catheter.
By using the construction according to the invention, coating or heat shrinking PTFE on the outside diameter of the one or more electrically conductive members will improve tracking of the device, and heat shrinking layers of PTFE, braid or coil imbedded in a polymer layer, or other polymers in telescoping fashion from proximal to distal end will yield a shaft with a stiffer, more manageable, proximal end and a softer, more maneuverable, distal tip.
The invention accordingly provides in a presently preferred embodiment for a variable stiffness electrically conductive composite resistive heating catheter shaft for placement within the vascular system, and the invention is particularly adaptable for use within a tortuous, small diameter vessel such as those found in the vasculature of the brain. The variable stiffness electrically conductive composite resistive heating catheter shaft comprises at least one electrically conductive member having a proximal end and a distal end, and at least one coaxial layer of a polymer, metal, or both for providing a desired additional stiffness extending over the at least one electrically conductive member, to thereby provide desired variations in stiffness along the length of the shaft. In one presently preferred embodiment, the variable stiffness electrically conductive catheter shaft comprises a plurality of coaxial layers of heat shrink polymer encapsulating the at least one electrically conductive member, the coaxial layers extending from the proximal end of the at least one electrically conductive member toward the distal end, the plurality of coaxial layers having different lengths to provide the electrically conductive catheter shaft with varying stiffness over the length of the electrically conductive catheter shaft. The plurality of coaxial layers can be arranged in successive progressively shorter coaxial layers, and can be formed of heat shrink polymeric material, such as polytetra fluoro ethylene (PTFE) polyethylene terephthalate (PET), polyether ethel ketone (PEEK), poly phenylene sulfide (PPS), or any of a variety of other polymers which can be fabricated into a structure and necked or shrunk over a shaft. A layer of braid or coil may also be embedded in the polymer to increase the stiffness of the composite shaft in certain areas.
While the invention can effectively use tubes which are placed over the exterior of the electrically conductive catheter shaft and then heat shrunk or bonded by adhesive to the at least one electrically conductive member, it is also contemplated that the shaft can be reinforced by other longitudinally extending additional structures with varying cross sections for certain specific applications.
In a presently preferred embodiment, the variable stiffness electrically conductive composite resistive heating catheter shaft comprises a first coaxial layer of a heat shrink polymer extending essentially the entire length of the at least one electrically conductive member, from the proximal end to the distal end; a second layer of a coaxial layer of a heat shrink polymer, of the same or different material as the first c

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